Faraday cage - suppressing stray EM fields

You have to love the variety of posts at Audiogon. Back to back posts today, one is asking which side of an ac plug is hot and the next post is hyperphysics.

I am not certain I understand this question as asked or if I am simply to stupid to understand it no matter how asked. But, I do not think that the guy sitting in the Farady cage had to worry about the integrity of an AC music signal and associated issues passing through the contraption.

Faraday's law states that any change in the magnetic environment of a coil of wire will cause voltage to be induced in the coil and that the induced voltage (emf) in a coil is equal to the negative of the rate of change of the magnetic flux times the # of turns in the coil. Generally taking about the interaction of charge and magnetic field. Not sure you want to create all of this going on around wire carrying your music signal. Could be an impedance/inductance issue in there too.. eh?

The cure would be worse than the disease so to speak.

Why do I suddenly have a headache?

Sincerely, I remain (even more than usual)

You are talking about Faraday's Law and the phenonmenon
of induction.

The Faraday cage is different. It is an undergraduate
physics exercise. Compute the field interior to a
hollow spherical conductor in the presence of an external
charge: Always zero. That is why that guy at boston
museum can sit inside a wire cage and not get electrocuted
while the van der graff makes lightening all around him.
It is also why your car is a good place to be in an
electrical storm whether it has tires on it or not.

But thanks for responding, and I'm sorry for the head-ache.

Judith

Judit is correct, and the military and some high tech computer companies use the Faraday cage to protect against stray RF and EMI signals, particularly in sensitive testing situations.

To answer your question, yes the cage could work, especially around (say) a turntable where you wish to isolate the phono cartridge and tonearm wires from picking up CB radio, FM broadcasts and the like. As far as cable goes, many of the Belden and Canare cables do feature a foil and/or copper mesh that in fact acts as a shield for just such purposes. The Faraday cage is just a large version of this same idea.

In any case, the cage or shield must be properly grounded, so the signal will dissipate to earth, rather than continually dancing around the outside of the metal shield.

Dear Clueless. Third line of third paragraph.... when you differentiated magnetic flux with respect to time...that was probably the start of your headache..lol

Thanks for the explanation Judith. No headache.

I remain,

FWIW, i have my sweetspot chair enclosed in a faraday cage. i lower myself in with a system of pulleys and chains and then close the hatch behind me. it's hard to discern the advantages. but, i've not once been struck by lightening whilst listening to my kit. (threw that last bit in for our friends from the uk.) -cfb

Kelly, your either hallucinating again or playing on the "hollow deck" of the Starship Enterprise. Beam me up, Scotty... : ) Sean
>

The Faraday Cage is used today in some Audio gear for shielding. The Dodson DA217MKIID DAC has a Faraday Cage located inside its enclosure.